1. Field of Invention
The present invention relates to a heart-sound detecting apparatus which can accurately determine a start point of a first heart sound I of a living subject, and a pulse-wave-propagation-velocity-relating information obtaining system using the heart-sound detecting apparatus.
2. Description of Related Art
A first heart sound I as one of a plurality of heart sounds produced by the heart of a living subject occurs upon closure of mitral valve and tricuspidalis valve. Accordingly, the first half portion of the first heart sound I includes, as a major component, closure sounds of mitral valve and triculspidalis valve, while the second half portion of the first heart sound I includes a component resulting from opening of aortic valve, which overlaps the first half portion of the first heart sound I resulting from the closure of mitral valve and tricuspidalis valve.
The heart sounds are influenced by internal noise such as blood-flow sound, and background or external noise which occurs outside the living subject. Accordingly, a waveform of heart-sound signal which represents the first heart sound I has a complicated shape, making it difficult to accurately determine a start point of the first heart sound I.